How's 4 tools sound instead? I could add one more, but I wouldn't consider it "essential".
1. Some sort of text editor that you know how to use.
2. Some sort of versioning that you know how to use.
3. Some sort of way to transfer files offsite that you know how to use.
4. Some sort of way to run the code. A local copy of the server environment that you use should do.
I can't think of anything else that's essential. Some things might help make you more productive, but you could easily continue working without the likes of Quicksilver or Spaces.
